Cordless tools including interchangeable battery units are widely known in the prior art, as exemplified for example by U.S. Pat. Nos. 3,043,996; 3,381,636; 3,533,119; 3,186,878; and 3,757,194. However, the general conception of the ultimate product employed in each of these patents has been that of simply substituting a packaged battery-type source of energy as an alternative to the conventional line cord set provided with corded power tools. Thus, the structures described by these patents essentially describe completed, self-contained tools with a receptacle provided therein for receiving the battery.